Q: A 422 N block sits on a table connected by a massless rope over a pulley to a hanging mass $$M. $$The coefficient of static friction between the block and the table is $$\mu_s = 0.75. $$What is the maximum value of $$M$$ such that the block remains stationary? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

$$M = \frac{0.75 \times 422}{9.8} = 32.3 \, \mathrm{kg}$$

Q: A 5 kg object is in an elevator accelerating upward at $$2 \, \mathrm{m/s^2$}. $$What is the apparent weight of the object? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

$$W_{app} = m(g + a) = 5 \times (9.8 + 2) = 59 \, \mathrm{N}$$

Question 1

Which of the following best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

Question 2

A 10 kg box is at rest on a horizontal frictionless surface. A force of 50 N is applied horizontally. What is the acceleration of the box? Use $$F = ma.$$

Accepted Answer

$$a = 5 \, \mathrm{m/s^2$}$$

Question 3

Which of the following is NOT a property of the gravitational force according to Newton's Universal Law of Gravitation?

Accepted Answer

It is always repulsive.

Question 4

A 60 kg box is placed on a frictionless ramp inclined at $$30^\circ to $$the horizontal. What is the normal force acting on the box? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

Accepted Answer

$$F_N = (60)(9.8)\cos 30^\circ = 509 \, \mathrm{N}$$

Question 5

A 50 kg ice skater pushes a 70 kg skater with a force of 40 N on frictionless ice. What is the acceleration of the 50 kg skater?

Accepted Answer

$$a = \frac{40}{50} = 0.80 \, \mathrm{m/s^2$}$$

Question 6

Which of the following statements about mass and weight is correct?

Accepted Answer

Mass is constant regardless of location, but weight depends on the local acceleration due to gravity.

Question 7

A 71 kg crate is pulled with a force of 300 N at an angle of $$40^\circ$$ above the horizontal on a frictionless surface. What is the horizontal component of the force?

Accepted Answer

$$F_x = 300 \cos 40^\circ = 230 \, \mathrm{N}$$

Question 8

If the net force on an object is zero, which of the following must be true?

Accepted Answer

The object is either at rest or moving at constant velocity.

Question 9

A 422 N block sits on a table connected by a massless rope over a pulley to a hanging mass $$M. $$The coefficient of static friction between the block and the table is $$\mu_s = 0.75. $$What is the maximum value of $$M$$ such that the block remains stationary? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

Accepted Answer

$$M = \frac{0.75 	imes 422}{9.8} = 32.3 \, \mathrm{kg}$$

Question 10

Which of the following is a correct statement about inertial and non-inertial reference frames?

Accepted Answer

Newton's Laws are only valid in inertial reference frames.

Question 11

A 5 kg object is in an elevator accelerating upward at $$2 \, \mathrm{m/s^2$}. $$What is the apparent weight of the object? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

Accepted Answer

$$W_{app} = m(g + a) = 5 	imes (9.8 + 2) = 59 \, \mathrm{N}$$

Question 12

Which of the following best explains why you feel lighter in an elevator accelerating downward?

Accepted Answer

The normal force (apparent weight) is less than your actual weight.

Question 13

A 185 N block and a 422 N block are connected by a massless rope over a frictionless pulley. What is the acceleration of the system? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

Accepted Answer

$$a = \frac{422 - 185}{422 + 185} 	imes 9.8 = 3.5 \, \mathrm{m/s^2$}$$

Question 14

Which of the following is the correct formula for the gravitational force between two masses $$m_1$$ and $$m_2$$ separated by a distance $$r$$?

Accepted Answer

$$F = G \frac{m_1$ m_2$}{r^2$}$$

Question 15

A 60 kg block is at rest on an inclined plane at $$30^\circ to $$the horizontal. The coefficient of static friction is $$\mu_s = 0.5. $$What is the minimum force required to start moving the block up the ramp? (Use $$g = 9.8 \, \mathrm{m/s^2$})$$

Accepted Answer

$$F = mg \sin 30^\circ + \mu_s mg \cos 30^\circ$$

Question 16

Which of the following is true about frictional forces?

Accepted Answer

Static friction is generally greater than kinetic friction for the same surfaces.

Question 17

A steel I-beam of weight 8.0 kN is lifted at constant velocity by two cables at $$70^\circ to $$the horizontal. What is the tension in each cable?

Accepted Answer

$$T = \frac{8000}{2 \sin 70^\circ} = 4256 \, \mathrm{N}$$

Question 18

Which of the following is a correct statement of Newton's Third Law?

Accepted Answer

For every action, there is an equal and opposite reaction.

Forces and Newton’s Laws: Structured Study Notes

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